Electrodeposition of zinc



Patented Sept. 10, 2946 Allen G. Gray, Rocky River, Ohio,

du Pont de Nemonrs & Company,

asalgnor to E. I. Wilmington,

M, a corporation of Delaware No Drawing. Application September 22, 1942,

Serial No. 459,288

14 Claims. (01. 204-55) This invention relates to the electrodeposition of zinc, and more particularly to acid plating compositions, baths, and processes for the electro''' deposition of zinc in the presence of an anthraquinone sulfonate.

Securing a good initial deposit in low current density areas upon an object being electroplated is often a diflicult problem. This diillculty, commonly referred to as lack of "covering power restricts the usefulness of many electroplating systems, since for satisfactory electroplating it is important that the object plated be covered over its entire surface with a deposit of relatively uniform thickness, and, with irregularly shaped objects, it is entirely unleaslble to distribute the current so as to avoid low current density areas.

Lack of covering power is an especially troublesome problem in electroplating such metals as cast iron and malleable iron, and it has, for instance, heretofore been considered impracticable to electroplate malleable or cast iron objects with certain metals or in certain otherwise advantageous electroplating baths on account of this deflciency.

The problem of securing adequate covering power at low' current densities is encountered at least to some extent in all systems for the electrodeposition of platable metals, but the need for a satisfactory answer to this problem has been particularly pressing in those systems where an important purpou of the electrodeposited metal is to protect the base metal against corrosion. Zinc is very resistant to corrosion, and accordingly with systems for the 'eleetrodeposition of zinc it is extremely important to have good covering power in all current density ranges; 7

Solutions for the electrodeposition of zinc may be broadly classified into two widely diflerent categories, namely, acid-zinc baths, such as those containing zinc sulfate, and cyanide-zinc baths, such as those containing zinc cyanide, as the electrolyte in each case. By means of suitable addition agents cyanld -zinc baths havebeen improved in recent years so as I deposits in all practical current density ranges.

For some purposes such mirror-like deposits are not required and for these uses the somewhat less expensive acid-zinc baths would be suitable were it not for the fact that difllculty is encountered in securing good coverage at low current densities.

It is an object of the present invention to improve the covering power at low current densities of acid-zinc electroplating systems; A further object is to provide compositions and procto give bright, smooth- 2 esses for the production of dense, adherent, nonporous, and ductile electrodeposits oi. zinc which are readily deposited in low current density areas. A further object is to provide processes for electrodepositing zinc over a variety of current densities, including low current densities, on dlfllcultly platable objects such as irregularly shaped objects of cast or malleable iron. Further objects will become apparent hereinafter.

The foregoing and other objects of this invention are accomplished by processes in which zinc is electrodeposited in the presence or an anthraquinone sulionate and are further accomplished by electrodepositing compositions and solutions in which an anthraquinone sulfonate is present.

The processes and compositions of this invention are characterized by their ability to eflect deposition of zinc from acid baths over a wide range of densities. They are further characterized in that the deposits produced are dense, adherent, and of relatively uniform thickness. The applicability of such deposits to corrosion protection of base metals will be readily apparent.

Benefits are achieved according to the present invention with any acid-zinc plating baths, that is, baths having a pH lower than about 7. Acid-zinc electroplating baths may contain as the principal electrolyte, for instance, zinc sulfate or zinc chloride as shown in the examples below or may contain any other salt of zinc which is stable in acid solution and is sufllciently soluble to give a substantial supply of zinc ions, such as zinc sulfamate, zinc acetate, and zinc formate.

The baths may be acidic by reason of the presence therein of an acid zinc salt, such as zinc sulfate, or of other acid constituents such as aluminum sulfate or chloride or ammonium chloride, or of both an acidic zinc salt and another acidic constituent. The acidity need not be great; that is, the pH need not be extremely low, and may, for instance, desirably be in the range of from about 3.0 to 7.0. As already described, in

, such acid-'zinc systems, the difliculty of gettin adequate coverage at low current densities is more pronounced than in alkaline baths such as cyanide-zlnc baths and the benefits to be derived from the inclusion of an anthraquinone sulfonate are enhanced.

According to this invention any anthraquinone sulfonate may be employed in an electrodepositing composition. There may be used, for instance, monosulfonic acids, such as l-anthraquinone sulfonic acid or 2-anthraquinone sulfonic acid, or polysulfonic acids, such as 1,8-anthraquinone disulfonic acid or 2,7-anthraquinone disulfonic 3 acid. The bath-soluble salts of the sulionic acids, suchas sodium, potassium, or ammonium salts, or partial salts may suitably be used and because of their excellent solubility. ease of preparation, and ease or handling in dry form, the sodium salts of thesulionic acids may be preferred. The manner of adding the sulionlc acid is comparatively unimportant, since whether the addition agent is present as an acid, or as a salt, or as a partial salt, will depend upon the pH of the bath. For purposes of this description where reference is made to a sulfonate, it will be understood that this may be a salt or partial salt or the free acid. p

The amount 01 an anthraquinone sulfonate to include in an electroplating composition or bath will vary, depending upon the plating system involved, the metal being plated, the magnitude of effect desired, and other similar factors. "The amount can best be determined by a few simple tests in the particular bath to be used. In general it will be round that from about .05 to 5.0 grams per liter of anthraquinone sulfonate will be satisfactory.

Anthraquinone s'ulfonates may be used in acidzinc electroplating baths in combination with other addition agents with which they are compatible. As' such additional agents, there may be used colloidal materials such as glue, wetting agents such as alcohol sulfates or naphthalene sulfonates, anti-pit agents and similar ancillary materials. When a second addition agent is used, the amount of the second agent may be. considerably varied but ordinarily it should be present only in minor amount as, for instance, from about .1 to 1.0 grams per liter.

When reference is made herein to electrodeposition of zinc it will be understood that the zinc may be co-deposited with another metal or metals to produce alloys. The invention is applicable,'for instance, in the co-electrodeposition of zinc and nickel or cadmium.

The invention will be better understood by reference to the following illustrative examples:

Example I An acid-zinc plating bath was prepared as described in the transactions of the Electrochemi- 'cal Society, vol. 80, p. 390, having the following pH adjusted to 3.6. Temperature 25 C.

To this bath was added 0.2 g./l. of l-anthraquinone sodium sulfonate to obtain a bath of this invention. Copper test plates were electroplated in this bath at various current densities. It wa found that complete coverage of the test plate with zinc was efiected in oneminute at all current densities including current densities as low as 0.1 amp./sq. it. On the other hand similar test plates electroplated in the solution before the addition of l-anthraquinone sodium sulionate were not covered in one minute at current densities below about 2 to 3 amps. per square foot,

indicating that the inclusion of the anthraquinone sulfonate effected an improvement in the coverage at low current densities.

0 I 7 pH adjusted to 4.0-.

4 Example II An acid zinc plating bath was prepared as described in the transactions. of the Electrochemical Society, vol. 80, p. 390, having the following composition:

zine sulfate znsotvnlo) Ammonium chloride (N H401) Aluminum sulfate (Al:(S0|)a.l8Hg0) sag.

pH adjusted to 4.0. Temperature 25 C. I

To this bath was added 0.2 g./l. of l-anthraquinone sodium sulfonate. grained deposits were produced with excellent covering power.

Example III An acid zinc plating bath was prepared as described in the transactions or the Electrochemical Society, vol. 80, p. 390, having the following composition:

Zinc sulfate (ZnS 04.7Hz0) Aluminum chloride (AlCl;.6H;O) Sodium sulfate (-NmSO.)

be lb Qua:

Example IV An acid-zinc plating bath was Drepaled as described in the transactions of the Electrochemi- -cal Society, vol. 80, p. 390, having the following composition:

Zinc sulfate (ZnSOflHgO) Sodium acetate (N aC=HaOa3Hr0 Aluminum sulfate (Alg(SOi)|.l8HzO).

sa's

pH 3.5. Temperature 25 C.

To the bath was added 0.2 g./l. of l-anthraquinone sodium sulfonate. Smooth, dense light colored deposits were produced, with excellent covering power.

' Example V An acid zinc plating bath was prepared as described in the transactions of the Electrochemical Society, vol. 50, p. 211 with the following composition:

air. I Oz./ga.

Zinc chloride (ZnCl) 136 Ammonium chloride (NH4CI) 214 Aluminum chloride (AlClpGHzO) 1 20 Temperature 25 C.

To the bath was added 0.2 g./l, of anthraquinone sodium sulfonate to secure a' bath of this invention. Copper test plates were electroplated Smooth white fine in this bath at various current densities. The covering power obtained in this above chloride bath was about equal to that obtained from the sulfate type bath as described in Example 1. Fur. ther, the conductivity of this bath was much superior to the sulfate bath described in Example I. By ,use of the anthraquinone sulfonate in the above bath complete coverage was obtained at current densities as low as 0.1 amp/sq. it. in one minute, whereas similar plates electroplated in the solution before the addition of the l-anthraquinone sodium sulfonate were not covered under similar conditions at current densities of 2 or 3 amp/sq. ft.

Example VI An acid-zinc plating bath of the chloride type was prepared as described in the transactions of the Electrochemical Society, vol. 50, p. 211, with the following composition Zinc chloride (ZnCh) 136 18 Sodium chloride (NaCl) 234 31 Aluminum chloride (AlCh.6H;O) 20 3 empe rature 26 0.

Smooth, uniform, white dense zinc deposits were produced with excellent covering power at current densities up to 100 amps/sq. ft. in unagiuring or proportioning the separate constituents. While certain illustrative compositions and processes have been shown, it will be understood that the invention is not limited thereby but that one skilled in the art, without departing from the spirit of the invention, may. readily devise numer ous compositions and processes for the electro deposition of zinc in the presence of an anthraquinone sulfonate.

I claim: a

1. In a process for the electrodeposition of zinc, the step comprising effecting electrodeposition of zinc from an aqueous acid-zinc electrodepositing solution in the presence of about from .05 to 5.0 grams per liter of l-anthraqiinone sodium sulfonate. I I

2. A zinc electrodepositing composition in dry form, comprising a zinc compound and an an-- form. comprising zinc sulfate and an anthraquinone sulfonate, the proportions of anthraquinone sulfonate and other constituents being such that when the composition is dissolved in water to make a solution of suitable concentration for electroplating the anthraquinone sulfonate is present in the solution at a concentration of from .05 to 5.0 grams per liter.

4. A zinc electrodepositing composition in dry form, comprising zinc chloride and an anthraquinone sulfonate, the proportions of anthraquinone sulfonate and other constituents being such that when the composition is dissolved in water to make a solution of suitable concentration for electroplating the anthraquinone sulfonate is present in the solution at a concentration of from 0.5 to 5.0 grams per liter.

5. A zinc electrodepositing composition in dry form, comprising zinc sulfamate and an anthraquinone sulfonate, the proportions of anthraquinone sulfonate and other constituents being such that when the composition is dissolved in water to make a solution of suitable concentration for electroplating the anthraquinone sulfonate is present in the solution at a concentration of from 0.5 to 5.0 grams per liter.

6; A zinc electrodepositing composition in dry form, comprising a zinc compound and l-anthraquinone sodium sulfonate, the proportions of anthraquinone sulfonate and other constituents being such that when the composition is dissolved in water to make a solution of suitable concentration for electroplating the anthraquinone sulfonate is present in the solution at a concentration of from .05 to 5.0 grams per liter.

7. An aqueous zinc electrodepositing solution comprising a zinc compound and about from .05 to 5.0 grams per liter of an anthraquinone sulfonate and having a pH lower than 7.0.

8. An aqueous zinc electrodepositing solution comprising a zinc sulfate and about from .05 to 5.0 grams per liter of an anthraquinone sulfonate and having a pH lower than 7.0.

9. An aqueous zinc electrodepositing solutioncomprising a zinc chloride and about from .05 to 5.0 grams per liter of an anthraquinone sulfonate and having a pH lower than 7.0.

10. An aqueous zinc electrodepositingsolution comprising a zinc sulfamate and about from .05 to 5.0 grams per liter of an anthraquinone sulfonate and having a pH lower than 7.0.

11. An aqueous zinc electrodepositing solution comprising a zinc compound and about from .05 to 5.0 grams per liter of I-anthraquinone sodium sulfonate and having a pH lower than 7.0.

12. In a process for the electrodeposition of zinc. the step comprising eflecting electrodeposi. tion of zinc from an acid-zinc electrodepositing bath in the presence of about from 0.05 to 5.0 gramsper liter of an anthraquinone sulfonate.

13,. In a. process for the electrodeposition of zinc, the step comprising eflecting electrodeposition of zinc from an acid-zinc electrodepositing bath comprising zinc sulfate as the principal elec- 'trolyte, in the presence of about from 0.05 to 5.0

grams per liter of an anthraquinone sulfonate.

14. In a process for the electrodeposition of zinc, the step comprising efiecting electrodeposition of zinc from an acid-zinc electrodepositing bath comprising zincchloride as the principal electrolyte, in the presence of about from 0.05 to ALLEN a. can. 

